Method for manufacturing el display apparatus

ABSTRACT

The present disclosure relates to a method for manufacturing an EL display apparatus including a light-emitting portion in which a light emitting layer is disposed between a pair of electrodes, a thin film transistor array device for controlling light emission of the light-emitting portion, and an EL display panel in which a plurality of pixels of colors of R, G, and B are disposed. After production of the EL display panel, an inspection step is performed to apply, to each of the pixels, a voltage which is preset for each of the colors of R, G, and B of the pixels, the voltage applied in the inspection step is a potential difference that is a reverse bias voltage opposite to an anode voltage and a cathode voltage during lighting, and the potential difference allows a faulty pixel to turn to a dead dot.

TECHNICAL FIELD

The present disclosure relates to a method for manufacturing an ELdisplay apparatus including electroluminescent (hereinafter, referred toas “EL”) elements which use organic materials as light-emittingmaterials and are arranged like a matrix.

BACKGROUND ART

An EL display apparatus including a plurality of EL elements that emitlight and are arrayed does not require backlight, and places nolimitations on a viewing angle, and therefore is under development as animage display apparatus of the next generation.

In the EL display apparatus, the EL element is a current-drivenlight-emitting element whose brightness is controlled by an amount ofcurrent passed there through. A passive matrix type and an active matrixtype are provided as methods for driving the EL elements. Although thepassive matrix method has simple pixel circuits, it is difficult toachieve a large-scaled and high-definition display. For this reason, inrecent years, an EL display apparatus of an active matrix type providedwith a drive transistor for each of the pixel circuits has formed amainstream.

The drive transistor and a peripheral circuit thereof are formedgenerally of thin film transistors using poly silicon, amorphoussilicon, or the like. The thin-film transistor is suitable for thelarge-scaled EL display apparatus because it is easy to fit for upsizingand inexpensive, although it has some drawbacks such as poor mobilityand large changes in the threshold voltage with time. Further, therehave been some studies also conducted for measures to overcome thechanges in the threshold voltage with time, which is a drawback of thethin film transistor, by working on the pixel circuits.

When the EL display apparatus of this type is manufactured, the thinfilm transistor in the pixel may be broken or damaged by electrostaticdischarge during the manufacturing process. Therefore, a panelinspection is performed during a manufacturing process as other displayapparatuses need it (see Patent Literature 1).

CITATION LIST Patent Literature

-   PTL 1: Unexamined Japanese Patent Publication No. 2010-176966

SUMMARY

The present disclosure relates to a method for manufacturing an ELdisplay apparatus including a light-emitting portion in which a lightemitting layer is disposed between a pair of electrodes, a thin filmtransistor array device for controlling light emission of thelight-emitting portion, and an EL display panel in which a plurality ofpixels of colors of R, G, and B are arranged. After production of the ELdisplay panel, an inspection step is performed to apply, to each of thepixels, a voltage which is preset for each of the colors of R, G, and Bof the pixels. The voltage applied in the inspection step is a potentialdifference that is a reverse bias voltage opposite to an anode voltageand a cathode voltage during lighting, and the potential differenceallows a faulty pixel to turn to a dead dot.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an EL display apparatus according to oneembodiment.

FIG. 2 is a perspective view illustrating an example of a pixel bank ofthe EL display apparatus according to one embodiment.

FIG. 3 is an electric circuit diagram illustrating a circuitconfiguration of a pixel circuit of the EL display apparatus accordingto one embodiment.

FIG. 4 is a schematic diagram illustrating wiring between a plurality ofpixels and individual wiring lines of the EL display apparatus accordingto one embodiment.

DESCRIPTION OF EMBODIMENT

Hereinafter, a method for manufacturing an EL display apparatusaccording to one embodiment will be described with reference to theaccompanying drawings.

Hereinafter, a description will be given of a thin film transistor arraydevice and an EL display apparatus using the same according to oneembodiment with reference to FIGS. 1 to 4. As illustrated in FIGS. 1 to3, the EL display apparatus is configured as a laminated structureincluding, sequentially from a bottom layer, thin film transistor arraydevice 1 having a plurality of thin film transistors; and an EL elementserving as a light-emitting portion formed of anode 2 which is a lowerelectrode, EL layer 3 which is a light-emitting layer formed of anorganic material, and cathode 4 which is transparent and an upperelectrode.

Light emission of the light-emitting portion is controlled by the thinfilm transistor array device.

The EL element has a structure in which EL layer 3 is disposed between apair of electrodes of anode 2 and cathode 4, a hole transport layer islaminated between anode 2 and EL layer 3, and an electron transportlayer is laminated between EL layer 3 and transparent cathode 4.

This EL display apparatus is structured of a plurality of pixels 5 whichemits light of red, green, and blue and are arranged like a matrix, andeach of pixels 5 is configured of the EL element and pixel circuit 6that controls light emission of the EL element.

Further, thin film transistor array device 1 is connected to each ofpixels 5, and includes a plurality of gate wiring lines 7 that arearranged in rows, source wiring lines 8 as a plurality of signal wiringlines that are arranged in columns so as to cross gate wiring lines 7,and a plurality of power wiring lines (omitted in FIG. 1) that extend inparallel to source wiring lines 8. In other words, the EL displayapparatus is of an active matrix type in which display control isperformed for each of pixels 5 positioned at an intersection betweeneach of gate wiring lines 7 and each of source wiring lines 8.

As illustrated in FIG. 2, each of pixels 5 of the EL display apparatusis formed of sub-pixels 5R, 5G, and 5B representing red (R), green (G),and blue (B), respectively. A plurality of such sub-pixels 5R, 5G, and5B are arranged like a matrix on a display surface (hereinafter,referred to as “sub-pixel row”). Sub-pixels 5R, 5G, and 5B are separatedfrom one another by banks 5 a. Banks 5 a are formed such that ridgesextending parallel to gate wiring lines 7 and ridges extending parallelto source wiring lines 8 cross each other. Then sub-pixels 5R, 5G, and5B are surrounded by these ridges (i.e., they are in the openingportions of banks 5 a).

Anode 2 is formed, for each of sub-pixels 5R, 5G, and 5B, on aninterlayer dielectric film on thin film transistor array device 1 andinside the opening portion of bank 5 a. In a similar manner, EL layer 3is formed, for each of sub-pixels 5R, 5G, and 5B, on anode 2 and insidethe opening portion of bank 5 a. Transparent cathode 4 is formedcontinuously on the plurality of EL layers 3 and banks 5 a in a mannerto cover all of sub-pixels 5R, 5G, and 5B.

Further, each of pixel circuits 6 is formed for each of sub-pixels 5R,5G, and 5B in thin transistor array device 1. Each of sub-pixels 5R, 5G,and 5B and each of pixel circuits 6 corresponding thereto areelectrically connected to each other by a contact hole and a relayelectrode which will be described later. Sub-pixels 5R, 5G, and 5B havean identical structure except that colors of emitted light of EL layer 3are different. For this reason, sub-pixels 5R, 5G, and 5B are notdistinguished from one another and described as pixel 5 hereinafter.

As illustrated in FIG. 3, each of pixel circuits 6 is configured of thinfilm transistor 10 functioning as a switching element, thin filmtransistor 11 functioning as a drive element, and capacitor 12 storingdata to be displayed in a corresponding pixel. EL element 13 isconnected in series to source electrode 11 s and drain electrode 11 d ofthin film transistor 11.

Then gate wiring line 7 is connected, for each raw, to gate electrode 10g of thin film transistor 10 functioning as a switching element includedin each of pixel circuits 6. Source wiring line 8 is connected, for eachcolumn, to source electrode 10 s of thin film transistor 10. One ofpower wiring lines, i.e., power wiring line 9 a, is connected, for eachcolumn, to drain electrode 11 d of thin film transistor 11 of each ofpixel circuits 6, and the other of the power wiring lines, i.e., powerwiring line 9 b, is connected to EL element 13.

Thin film transistor 10 is formed of gate electrode 10 g connected togate wiring line 7, source electrode 10 s connected to source wiringline 8, drain electrode 10 d connected to capacitor 12 and gateelectrode 11 g of thin film transistor 11, and a semiconductor film (notillustrated). When a voltage is applied between gate wiring line 7 andsource wiring line 8 which are connected to thin film transistor 10,thin film transistor 10 stores a voltage value as a display data of thevoltage applied to source wiring line 8 in capacitor 12.

Thin film transistor 11 is configured of gate electrode 11 g connectedto drain electrode 10 d of thin film transistor 10, drain electrode 11 dconnected to power wiring line 9 a and capacitor 12, source electrode 11s connected to anode 2, and a semiconductor film (not illustrated). Thinfilm transistor 11 supplies a current corresponding to the voltage valueof the voltage stored in by capacitor 12 from power wiring line 9 a toan anode side of EL element 13 through source electrode 11 s.

This means that cathode voltage Vss is applied to a cathode terminal ofEL element 13 from power wiring line 9 b, and anode voltage Vdd isapplied to an anode terminal of EL element 13 from power wiring line 9 athrough thin film transistor 11. Anode voltage Vdd and cathode voltageVss are set in such a relation that anode voltage Vdd is larger thancathode voltage Vss.

As illustrated in FIG. 4, ESD (Electrostatic Discharge) protectionelement 14, as a nonlinear resistance element, is connected to each ofgate wiring lines 7 each of which is connected to each of pixels 5 of R,G, and B. In addition, ESD protection element 15 is connected to each ofsource wiring lines 8R, 8G, and 8B of each of pixels 5 of R, G, and B.

Referring to FIG. 4, reference numeral 17 represents an electrodeterminal of gate wring line 7, reference numerals 18R, 18G, and 18Brespectively represent electrode terminals of source wiring lines 8R,8G, and 8B, and reference numerals 19 a and 19 b respectively representelectrode terminals of power wiring lines 9 a and 9 b. During normallighting, anode voltage Vdd is applied to power terminal 19 a, andcathode voltage Vss is applied to power terminal 19 b in such a relationthat Vdd is larger than Vss. For example, in a case where anode voltageVdd=10 V of a high-voltage side, and cathode voltage Vss=0 V of alow-voltage side are applied. When only pixel 5 of R is to be lighted,zero potential can be applied to electrode terminal 18R, and a positivepotential can be applied to other electrode terminals 18G and 18B.

As a result of studying a method for inspecting a defect of a pixelduring the manufacturing step of an EL display apparatus, it is foundthat a potential defect which will occur in the future can be detectedin advance through screening for a dead dot by applying, to each ofpixels 5, a reverse bias voltage where anode voltage Vdd is smaller thancathode voltage Vss.

In addition, it is also found that the number of the dead dotsincreases, and yet the numbers thereof are different from one anotheramong R, G, and B by increasing a potential difference of the reversebias voltage to be applied.

The reason for these phenomena can be this: by applying the reverse biasvoltage, in a case where a foreign object is present in the pixel, anelectric field is concentrated by the foreign object, leakage is causedin a portion where a film thickness is small in each of the layers thatform an EL display panel. The pixels thus turn to the dead dots. On topof that, magnitudes of potential differences of the reverse biasvoltages differ from each other depending on differences in the materialfor EL layers of R, G, B. These reverse bias voltages individually causethe dead dots for the pixels of R, G, B. As a specific example, reversebias voltages between 10 V and 30 V are applied as cathode voltage Vsson the low-voltage side while anode voltage Vdd on the high-voltage sideis set to 0 V. As a result, it is found that the following screeninginspection can be done: a dead dot is caused for the pixel of G at areverse bias voltage of about 20 V, for the pixel of B at a reverse biasvoltage of about 25 V, and for the pixel of R at a reverse bias voltageof about 30 V.

According to the manufacturing method of the present disclosure, aninspection step is provided after the EL display panel is produced. Theinspection step includes applying a reverse bias voltage which is apotential difference serving as a reverse bias voltage opposite to theanode voltage and the cathode voltage during lighting, and a magnitudeof the reverse bias voltage is set in advance for each of the pixels ofR, G, and B. The inspection step allows screening for a potential deaddot and a potential dim dot that will occur in the future, in advanceafter the panel is produced, thereby reducing defectives due to faultypixels after the production, and improving yields of the EL displayapparatus during the production.

As described above, according to the present disclosure, an inspectionstep of applying a reverse bias voltage to each of the pixels isprepared after the production of the EL display. The inspection stepperforms screening in advance for a potential dead dot and a potentialdim dot that will occur in the future, reduces occurrences of a faultyproduct caused by a faulty pixel after production, and improvement ofthe yields of the EL display apparatus during the production.

INDUSTRIAL APPLICABILITY

The present disclosure is useful for improving the yields during theproduction of the EL display apparatus.

REFERENCE MARKS IN THE DRAWINGS

1 thin film transistor array device

2 anode

3 EL layer

4 cathode

5 pixel

6 pixel circuit

7 gate wiring line

8, 8R, 8B, 8G source wiring line

9 a, 9 b power wiring line

10, 11 thin film transistor

13 EL element

1. A method for manufacturing an EL display apparatus, the displayapparatus comprising: a light-emitting portion in which a light emittinglayer is disposed between a pair of electrodes; a thin film transistorarray device for controlling light emission of the light-emittingportion; and an EL display panel in which a plurality of pixels ofcolors of R, G, and B is disposed, the method comprising: performing,after production of the EL display panel, an inspection step ofapplying, to each of the pixels, a voltage which is preset for each ofthe colors of R, G, and B of the pixels, wherein the voltage applied inthe inspection step is a potential difference that is a reverse biasvoltage opposite to an anode voltage and a cathode voltage duringlighting, and the potential difference allows a faulty pixel to turn toa dead dot.